It is nowadays well known that sleeping in a supine position significantly reduces the risk of SIDS [25], [26], [27]. Since the “back to sleep campaign” launched in 1992 by the American Academy of Pediatrics, all pediatricians suggest to the parent to place their children on their back when they sleep in the first year of life; as a consequence, the occurrence of SIDS has been greatly reduced (from 1.4 per 1,000 live births in 1988 to 0.55 per 1,000 live births in 2003). However, the causes of SIDS mainly remain undiscovered, and its incidence is even nowadays beyond 0.5 per 1000 births. Moreover, probably because of the predominant supine sleeping position, the occurrence of positional plagiocephaly has tremendously increased since 1992. This is probably associated to the fact that, because of a repetitive pressure applied to the soft infant head bone, for instance during the sleep, the infant skull changes its shape [24], [25]. In this case, some helmets are sometimes applied to correct the shape of the skull, but their efficacy is questioned [28], [29]. A more common solution suggested by the pediatricians is to adopt a strategy of “repositioning”, in other words try to make sleep the children on a side (the opposite with respect to the compressed skull area) as long as possible.
Some special pillows [30] can be used to this scope, but it is clear that a continuous supervision cannot be performed; in this sense, the analysis of the infant orientation during the night can represent a significant instrument, both to prevent the outcome of plagiocephaly and to control the efficacy of the infant repositioning strategy.
Different systems have been proposed for monitoring the breath of an infant, with the aim of preventing the occurrence of SIDS.
The most reliable of them adopts costly technologies, which can be used only by skilled people in a clinical scenario. For instance, in [1, 2] some devices which analyze the levels of O2 and CO2 in the infant breath are disclosed; in [3, 4], a pulse oxymeter is mounted onto the feet of the infant for measuring the blood oxygen and heart pulse rate; other systems are based on electrodes [5], air mattresses equipped with pressure sensors [6], measurements of the room and expired breathe humidity [7]; video systems [8, 9] or constellation of different kinds of sensors [10, 11] have also been exploited: these permit the infant orientation to be estimated, which is an important factor in evaluating the risk of SIDS, as it has been demonstrated that infants sleeping in a supine position have a lower risk of SIDS with respect to infants sleeping in prone position. However, it should be clear that, because of their complexity and cost, these systems cannot be adopted in the normal home scenario by untrained people.
More easy-to-use systems have been proposed to this scope. Most of them are based on a sensorized pad [12], which has to be positioned under the mattress; because of its simplicity and low cost, this kind of systems is widely diffused, at least in Italy (see Angelcare® by Foppapedretti [13]). However, this approach suffers some significant drawbacks: the system is not easily transportable, as is has to be removed from under the mattress and repositioned if necessary; moreover, in the case when the infant moves during the sleep (very frequently occurring after the sixth month of life), he can shift with respect to the sensor area; in this case, the system cannot detect the infant movements and a false alarm is generated.
This can contribute to generate a status of anxiety in the caregivers that suddenly weak up in the night, and bring them after a significant number of false alarms to a lack of confidence in the monitoring system and consequently to abandon it.
Wearable/contact sensors represent a more reliable choice with respect to the problem of the false alarms. In [14], pressure and temperature transducers are used to estimate the infant attitude and to detect possible SIDS events; a transmitter/receiver pair is used to alert the caregiver of any risk situation. In [15] a marker based (and costly) video system is coupled with gravity sensors to estimate in real time the infant position; a signal is emitted when the infant is in a dangerous situation (for instance, prone sleeping) to force him to move in a different position. In [16] a device for monitoring the infant breath activity through a microphone is disclosed; however, ambient noise could represent a problem for this kind of system, leading to a potentially undetected SIDS event. In [17, 18, 19], a detector including a piezoelectric element is attached with a strap to the chest of the infant to detect its breath, and communicates an alarm to a receiver device in case of null detection; however, such system could be uncomfortable for the infant, or impractical for the parents each time the infant clothes have to be changed. A similar system, based on a trans-illuminated optical fiber, is described in [20].
Accelerometers can be used to construct wearable devices for breath monitoring. In [21], a pendant acceleration sensor, attached to the infant, communicates via wireless with a monitor device; in absence of movements (possible SIDS event), an alarm can be generated. In [22], an accelerometer-based system for controlling both animals and infants is described.
The inventors of [23] disclose an accelerometer-based system for detecting the lack of motion of an infant; the system is also capable to distinguish between different kinds of movements; when a lack of motion is detected, it stimulates the infant through a buzzer, with the aim of resuscitating him. The system is attached to the infant clothing, but no securing means is provided for avoid ingestion, which could represent a significant aspect for any wearable system composed by small pieces. A band pass filter, not including the DC component, is used to isolate the typical frequencies associated to breathing and movements. This can be a problem if one wants to estimate the infant orientation, which is in facts associated with the zero frequency component of the spectrum. Moreover, the housing of the sensor is rigid: this could be an uncomfortable situation for the infant. Lastly, a transmitter/receiver system is necessary to get the data from the sensor module.
Another accelerometer-based system for controlling the orientation and breathing of a sleeping infant is disclosed in [24]. Wireless technology is in this case necessary to guarantee that the sensor module can communicate the data to a different base module, which executes the data processing, and to the caregiver. In particular, it is highlighted that different communication channels (from Internet to the mobile phone net) can be used to alert the caregiver. Short data registration sequences, performed in a controlled environment (that is, when the caregiver can assure that the infant is sleeping and breathing), can be used in this case to optimize the sensor sensitivity (learning mode). Fast/Short Fourier Transforms, Auto Regressive models and Root Mean Squared are used to detect that the infant is breathing.
A skin temperature sensor is also included to assure that the sensor module is effectively attached to the infant body.
It appears evident from what above described that the prior art has in most part aimed to simply controlling in real time the breath (and sometimes also the orientation) position of an infant, to alert a caregiver when a potentially dangerous situation occurs related to a SIDS event.
It also appears evident that the prior art has proposed systems that can only be used in a controlled environment, such as a hospital bed or the bed in which the infant usually sleeps. Moreover, the existing commercial systems are usually composed by a set of at least two pieces (e.g. a sensor module and a data processing/alarm module), that are both necessary to guarantee the proper functioning of the system.
The prior art has anyway failed to propose an easily portable system, composed by a single piece, which can be comfortably worn by the infant with the assistance by the caregiver. Moreover, none of the cited prior art gives the possibility to record the breathing/positioning data for further processing. In this sense, none of them can provide useful indications about the long term SIDS risk, the possible outcome of plagiocephaly, or about the efficacy of the repositioning strategy.